Relationship between "Hardness/HRC" and "Toughness" and "Edge Retention"

[Slice-and-dice]

I really enjoy Larrin's work examining multiple steels and their properties. Anyone able to clarify how HRC relates to toughness and edge retention? Is the Rockwell hardness a measure of both? Just edge retention? Thanks for any input in imparting understanding.

 

[jfk1110]

Hardness \ edge retention and toughness are pretty much polar opposites......A good blade will have a mix of both.......to hard or high and its chips. Not tough enough and the edge will just.roll\ bend.

Simple explanation but its a bit more technical than that but essentially that is it....

 

[Tsujigiri]

The harder you make the blade, the less tough it is but the higher the edge retention is (unless you get to the point where chipping is an issue). Different steels trade off between toughness and edge retention differently, so that has to be taken into account when heat treating.

 

[Synov]

Hardness is resistance to permanent deformation. Toughness is ability to absorb energy and deform without breaking. A harder blade will be less likely to deform but more likely to break. So increasing the hardness of a steel will make it less tough, because it will break instead of deforming.

Carbides largely determine how hard a steel can get and how much edge retention it can have. Hard carbides resist deformation and wear from cutting, keeping the blade sharp. So increasing hardness increases the edge retention.

 

[shinyedges]

Tough- plastic deformation
Strong- ability to resist bending

Soft steels can be very tough but not strong. Hard steels can be strong and resist bending (like for prying) but won't deform, instead they break.

Like mentioned above, a nice balance is ideal. Though with modern cpm steels I think strength is over shadowing toughness.

Look at Nathan's d3v. It won't bend and take a set, but you'll have a hell of a time breaking it.


Edge retention goes up with hardness. Obviously many other factors play into edge retention like geometry, toughness and strength.


All of this is in general and in layman's terms.